Spark plug containing electrical resistor



March 9, 1965 H. M. DRESSEL SPARK PLUG CONTAINING ELECTRICAL RESISTORFiled Aug. 11, 1960 INVENTOR. f/'A/RV M. OQESSEL United States Patent 73,173,056 SPARK PLUG CONTAINING ELECTRICAL RESISTOR Henry M. Dressel,St. Marys, Pa., assignor to Staclrpole Carbon Company, a corporation ofPennsylvania Filed Aug. 11, 1960, Ser. No. 48,913 4 Claims. ((31.315-58) This invention relates to spark plugs, and more particularly tothose containing electrical resistors to prevent electrical interferencewith television reception.

Ordinary automotive spark plugs are instrumental in generating in theignition system high frequency electric currents that are in thetelevision broadcast bands and which therefore will interfere with boththe picture and the sound in television receiving sets when the vehiclecontaining the plugs is in the neighborhood of the sets. To prevent suchinterference, it is the general practice to insert an electricalresistor in the porcelain core of a spark plug. Such a resistor iseffective for its intended purpose, but usually not for the length oftime that the spark plug is used. The ends of the resistor are sprayedwith a material of low electrical resistance, generally Monel or nickel,to form low resistance end contacts that electrically connect theresistor to the center electrode and the upper terminal of the plug. Asthe plug is used in service, the air in the chamber containing theresistor is ionized and in time will cause the contacts to corrode andeven disappear. In some cases the ends of the resistance material itselfbecome deteriorated too. The result is that the electrical resistance ofthe resistor ultimately increases to a very great extent. This not onlykeeps the resistor from performing its intended function, but it alsointerferes with proper operation of the spark plug.

It is among the objects of this invention to provide a resistor sparkplug in which the useful life of the resistor is prolonged greatly.

In accordance with this invention an electrical resistor, having lowresistance end contacts, is disposed in a chamber in the tubularporcelain core of a spark plug. The resistor contacts are electricallyconnected with the inner ends of an electrode and a terminal, which aresealed in opposite ends of the core. Dielectric material is placed inthe chamber to exclude all air from the resistor contacts so that theywill not be alfected adversely. Preferably, all air space in the chamberis filled with a dielectric grease or the like that has high viscosityat both high and low temperatures.

The preferred embodiment of the invention is illustrated in theaccompanying drawing, in which the single figure is a side view of aspark plug, with the upper portion of the core shown in centrallongitudinal section.

Referring to the drawing, a conventional spark plug has a tubularporcelain core 1, the lower portion of which is sealed in a tubularmetal base 2 having a threaded lower end to permit it to be screwed intothe upper end of a cylinder in an internal combustion engine, such as anautomobile engine. A rod-like center electrode 3 extends lengthwise ofthe core and is sealed in its lower portion. The lower end of theelectrode projects a short distance below the metal base and is spacedfrom a second electrode 4 connected to the base to form the usual sparkgap. The upper end of the center electrode projects slightly into thelower end of an axial chamber 6 in the core. The customary electricterminal '7 is screwed into the upper end of the core and sealedtherein. Inside the chamber there is a cylindrical resistor having acarbonaceous body 8, on the opposite ends of which there are extremelythin contacts 9 that may be formed by applying low resistance materialto them, such as by 3,173,056, Patented Mar. 9, 1965 spraying Monel,nickel .or the like thereon. The upper contact is pressed against thelower end of terminal 7 by a coil spring 10 compressed between the lowerend of the resistor and the upper end of the center electrode 3. Theresistor spark plug described thus far is conventional.

It is a feature of this invention that oxidation or disappearance of theresistor contacts 9 is greatly retarded or eliminated by excluding airfrom them. This is done most conveniently by filling all of the airspace in chamber 6 around the resistor and the spring with a material12. having high dielectric strength. The material is poured or injectedinto the chamber in a liquid or plastic condition and should be viscousenough to avoid leaking from the plug. The properties of the materialshould be such that its viscosity will not be reduced appreciably at thehigh temperatures at which the plug operates. Various materials may beused for this purpose, one being grease such as Essos Nebula or ShellsDarina. Those greases have high dielectric strength and maintain theirviscosity at high temperatures. Oil can be used if one can be certainthat no leakage will occur. Dielectric synthetic plastics, such as DowCornings DC4, are satisfactory.

Dow Corning also sells a dielectric gel that can be used in a sparkplug. It is called Sylgard 51 and comes in liquid state. After beingmixed with a catalyst it is poured into the plug chamber, which is thenheated to convert the mixture into a gel.

Another unexpected result of this invention is that the substitution ofmaterial of high dielectric strength for the air in the core chamber 6materially increases the electrical capacitance of the spark plugbetween the grounded metal base 2 and the electrical conductors insidethe porcelain core, which helps to suppress the interference caused bythe radiations from the ignition cable connected to the plu It has beenfound that when the resistor contacts 9 are protected from thedeleterious efiects of ionization by eliminating air space around them,the resistor will last as long as the spark plug is likely to be used.There is very little change in the resistance of the resistor in 10,000miles of driving of a car containing such a plug.

According to the provisions of the patent statutes, I have explained theprinciple of my invention and have illustrated and described what I nowconsider to represent its best embodiment. However, I desire to have itunderstood that, within the scope of the appended claims, the inventionmay be practiced otherwise than as specifically illustrated anddescribed.

I claim:

1. In a spark plug, the combination with a tubular porcelain core, anelectrode sealed in one end of the core and projecting therefrom, anelectric terminal sealed in the opposite end of the core and projectingtherefrom, the core having an axial chamber between the inner ends ofthe electrode and terminal, a carbonaceous electrical resistor disposedin said chamber and having low resistance end contacts, and a coilspring compressed between the inner end of the electrode and theadjacent end contact of said resistor to electrically connect them andto press the opposite end contact of the resistor against the inner endof said terminal, of viscous dielectric material filling said chamberaround the resistor and excluding all air from said contacts to prolongthe useful life of the resistor.

2. In a spark plug according to claim 1, said dielectric material beinggrease.

3. In a spark plug according to claim 1, said dielectric material beinga dielectric gel.

3,1 3 4. In a spark plug according to claim 1, said dielectric materialhaving high viscosity at both high and low temperatures.

References Cited by the Examiner UNITED STATES PATENTS 1,927,297 9/33Rabezzana 31558.1 X 2,442,015 5/48 Peters et a1. 315-85 4 Brinson.Cipriani et a1 31558.1 Peterson 17484 Marks et a1. 315-58 Brown 17475 XDAVID J. GALVIN, Primary Examiner. ARTHUR GAUSS, Examiner.

1. IN A SPARK PLUG, THE COMBINATION WITH A TUBULAR PROCELAIN CORE, ANELECTRODE SEALED IN ONE END OF THE CORE AND PROJECTING THEREFROM, ANELECTRIC TERMINAL SEALED IN THE OPPOSITE END OF THE CORE AND PROJECTINGTHEREFROM, THE CORE HAVING AN AXIAL CHAMBER BETWEEN THE INNER ENDS OFTHE ELECTRODE AND TERMINAL, A CARBONACEOUS ELECTRICAL RESISTOR DISPOSEDIN SAID CHAMBER AND HAVING LOW RESISTANCE END CONTACTS, AND A COILSPRING COMPRESSED BETWEEN THE INNER END OF THE ELECTRODE AND THEADJACENT END CONTACT OF SAID RESISTOR TO ELECTRICALLY CONNECT THEM ANDTO PRESS THE OPPOSITE END CONTACT OF THE RESISTOR AGAINST THE INNER ENDOF SAID TERMINAL, A VISCOUS DIELECTRIC MATERIAL FILLING SAID CHAMBERAROUND THE RESISTOR AND EXCLUDING ALL AIR FROM SAID CONTACTS TO PROLONGTHE USEFUL LIFE OF THE RESISTOR.